Furnace, particularly adapted for producing ferric oxide from ferrous sulphate



Jan.

OXIDE FROM FERROU HARRISON ETAL FURNACE, PARTICULARLY ADAPTED FORPRODUCING FERR s SULPHATE Original Filed June l, 1939 Sheets-Sheet 2Jan. 6, 1942.

, A. HARRISON ET FURNACE, PARTICULARLY ADAPTED F OXIDE FROM FERROUS S I2,268,588 0R PRODUCING FERRIC ULPHATE Original Filed June l, -1939 :ssheets-sheet 3' Patented Jan. 6, 1942 UNITED STATES PATENT OFFICEFUBNACE, PARTICULABLY yADAPTED FOR PRODUCING FERBIC QXIDE FROM FER- ROUSSULPHATE Allen Harrison, Whiston, and Frederic Barnes Waldron, Present,England, assignors to Pilk' ington Brothers Limited, Liverpool, England,a limited-liability company of Great Britain Original application June1,- 1939, Serial No.

276,764. Divided and this application November 30, 1939, Serial No.306,782

(ci. zes-21) Claims.

This invention relates to a `furnace which is' particularly adapted forproducing ferrie oxide from ferrous sulphate or copperas. Y

As set forth in our copending application Serial No. 276,764, led June1, 1939, of which the instant application is a division, ferrie oxidehas a number of uses, among vwhich may be mentioned by way of example,the manufacture of plate glass wherein it is used as a polishing mediumand also the manufacture of paint, wherein it is used as afpigment. Whenused as a glass polishing medium, it is commonly termed rouge and mustbe free from gritty substances and other contamination so that noharmful results will befall the glass during the polishingprocess. Onesource of ferrie oxide is waste pickle liquor, that is. ferrous sulphateor copperas that has been formed from the acid used for pickling sheetsinthe tin plate mills. Several ways are known of converting the ferroussulphate to ferrie oxide, that most commonly employed being to dehydratethe ferrous sulphate in a muflie kiln and calcine the resultant ferroussulphate monohydrate to decompose it into ferrie oxide, sulphur dioxide,sulphur tri-oxide and perature and in the amount of heat employed andnecessitating frequent shutting down of the plant in order to removethecaked oxide. Laboratory investigation has shown that particles of ferricoxide will stick to themselves as well as to most materials attemperatures of '750 C.

In the improved muifie furnace or kiln, the ferrous sulphate monohydrateis deposited at the centre of a turntable hearth located in a calciningchamber and gradually moved to the periphery of the table by a series ofrabble bars located above the table. During its excursion from thecentre to the periphery 'of the table the charge of monohydrateundergoes calcination and is decomposed into ferrie oxide, sulphurdioxide, sulphur trioxide and water. The ferrie oxide is scooped on thetable at its outer edge and dropped into a chute leading to the outsideof the furnace. The evolved gases are passed rst to a lime tower, andthence to the atmosphere.

The surface of the turntable or hearth as well water. The production ofrouge by this method able 'period, in a settling tank to allow gritty lsubstances to settle out.

, ne of the important features of the present plate works are as therabble bars are made of metal in order that there be no contaminationfrom this source. Since the rabble bars,v in-,co-operation with therotation of the hearth, positively actuate the material kundergoingtreatment, outwardly to" ward the periphery of the table, sticking ofthe ferrie oxide to the table is prevented. Such sticking is alsoprevented by effecting calcination solely through the use of radiantheat. For this purpose. the calcining chamber is enclosed at the top bya metal dome exteriorly heated by the combustion of raw producergas and,because the dome is metal, the trouble due to spalling of a refractoryarch'with its accompanying depositing of gritty material in the charge,yis elimihated. All of the metal parts that are subjected inventionresides'in the meansprovided 'foreliminating the rst mentioned source ofcontamination, namely, that from the refractory material of the kilns inwhich the monohydrat'e is lcalcined. 'I'his has been accomplished by aspecial furnace construction wherein all the parts that might be asource of contamination are made of metal. Early experiments conductedwith a rotary inclined type all-metal kiln exteriorly heated, met withlittle success, one of the chief reasons being that, at the temperaturesmet with in the production of ferric oxide for rouge (i. e.,temperatures in the neighbourhood of 885 C.), substantial caking on thewalls ofthe kiln occurred, requiring considerable increases in temtohigh temperature' are made of a special steel.

,the only one found satisfactory to withstand condions in the calclningfurnace being Vesuvius steermanumctured by fifths-Vickers stainlessSteels, Limited.

According to other features of the invention,

lmeans are provided for accommodating the exg pension and contraction ofthe metal parts sub-A ject to high temperatures, and for isolating theturntable driving mechanism from the temperatures and acid conditions ofthe calcining'chamber. These and other features of the invention will beevident as the description of the invention proceeds.

Referringto the drawings: Figure 1 is a vertical cross-sectional view ofa furnace equipped with the present improvements and particularlysuitable for carrying out the improved process;

Figure 2 is a horizontal sectional view on line 2-2 of Figure 1;

Figure 3 is a partial vertical sectional view on line 3-3 of Figure 2and showing in detail the construction of and the means for suspendingtherabble bars;

Figure 4 is a. partial vertical sectional view on line 4 4 of Figure 2and showing in detail, the means for isolating the mechanism forrotating the turntable hearth from the calcining chamber;

Figure 5 is a diagrammatic View of a portion of the apparatus forcarrying out that phase of the process with which the instant inventiondeals.

Figure 6 is a side view of one of the rabbles H as seen from the rightin Figure 3, on an enlarged scale; and

Figure 7 is a view of the same from below.

As previously stated, the first step in the process of converting wastepickle liquor to ferrie oxide metal dome D and terminating at its lowerend just above a turntable hearth F. This turntable divides the circularcentral chamber C into an upper calcining chamber G and a lower chamberG1 wherein there are located the devices for .effecting the rotation ofthe turntable.

The turntable hearth itself (see Figures l, 3 and 4) includes in part anupper circular metal plate F1 made in two concentric parts with anintermediate joint F2 to provide for expansion and contraction. Theturntable further includes a lower casting F3 and a series ofintermediate involves freeing the liquor of the contained impurities asit comes from the tin plate mills. This step is effected by dissolvingthe ferrous sulphate in tanks in the presence of iron to take up .anyfree acid that may be present. The solution is then blown into a leadlined settling tank maintained by steam pipes at a temperature ofapproximately 60 C., thus enabling a highly concentrated solution to beobtained. The solution then enters an atomizing chamber A (Figure 5)under a.l constant head in which chamber the ferrous sulphate is reducedto monohydrate frm. Insofar as an understanding of the present inventionis concerned, the details of the apparatus for converting the ferroussulphate to ferrous sulphate monohydrate need not be described, but if adescription thereof is desired, reference may be had to U. S. Patent No.1,607,206, issued to O. S. Neill, November 16, 1926. Sufiice. it to say,monohydrate ferrous sulphate collects in the form of small spheres atthe bottom of the atomizing chamber A, from which it is fed through themedium of a turntable A1, driven at a suitable speed, to a pipe A2leading to a hopper B locatedat the top of a calcining furnace C (seeFigure 1).

The calcining furnace C (Figures 1 and 2) includes a central circularchamber C1, defined by vertical walls C2 formed-of suitable refractorymaterial, and a top consisting of a metal dome D to which furtherreference will be made later on.' The furnace further includes outerwalls C3 and arched top C4 which are of usual furnace construction,these walls at two sides of the furnace and at the top thereof beingspaced from the outer surfaces of the walls and dome defining thecircular chamber C in order to provide a pas- The circulation of thecombusfurnace wall at about the level of the dome in order that a checkmay be had upon combustion conditions. A steel frame-work consisting ofvertical and of horizontal members C8 is provided for the purpose ofsupporting certain elements in the furnace hereinafterde'scribed.

As previously stated, the ferric sulphate monohydrate is introduced intothe furnace from the hopper B, through a verticaltube E extending fromthe top of the furnace down through the layers of refractory materialF4, the whole being joined together by vertical bolts F5 so that theturntable will rotate as a unit. The lower member F3 of the turntable isformed with ribs f for strength and is provided with a flange f1 restingupon a complementary flanged element f2 fixed at the top of a verticalshaft f3 supported at its lower end by a thrust bearing f4. Likewise onthe vertical shaft there is fixed a bevelled gear f5, the hub portion ofwhich is suitably journalled to maintain the shaft in its verticalposition, the bevel gear being driven through means not shown to effectrotation of the turntable. y

Near its outer periphery, the overall thickness of the turntableissomewhat greater than the overall thickness in its centre portion, andthis thicker portion of the hearth moves in an annular channel F6 formedby the side wall C2 of the chamber, a horizontal shelf C9 presented bysuch side wall and a vertical cylindrical element F"I supported in asuitable manner and extending up beyond and within the confines of theouter thicker portion of the' turntable previously referred to. Someloose material F8 such as sand or diatomaceous earth capable ofwithstanding high temperatures is contained in the channel F6 and actsas a seal to prevent the passage of heat and oxides of sulphur from thecalcining chamber above the turntable to the chamber below the turntablewherein lthe mechanism for rotating the latter is contained, thepurpose, of course, being to prevent any detrimental effect that theheat or gases might otherwise have on the metal of which the drivingmechanism is made.

In the charging of the furnace, the ferrous sulphate monohydrate, passesdown the central tubular element E, and is deposited on the centre ofthe turntable which is rotated in a clockwise direction looking at theparts from the top (see Figure 2). As the table rotates, a series ofrabbles H- overlying the table gradually moves the material from thecentre of the table outwardly towards the periphery thereof. Theserabbles are best shown in Figures 2 and 3 and on an enlarged scale inFigures 6 and 7. It will be noticed that the rabbles vary in length, thearrangement being such that when any portion of the material on thetable engages a given rabble, such material will, as the table continuesto rotate, be pushed by the rabble, depending upon its length, adistance outwardly toward the aeeasas tical portion H2 located at anangle with respect to a tangent to the table at the point where thescraper is located, andwhich .slants progressively outwardly, theleading edge of the scraper being within the periphery of the table andthe trailing edge without the periphery thereof. This scraper acts toforce the nished ferrie oxide off the table and into a chute H3 throughwhich the material passes to the outside of the furnace. The scraperelement further includes a triangular shaped upper section H'1 with ladepending bifurcated portion H5 at its outer end resting upon a bar HBextending between two block supports H7. supported by the bar H6 and bythe turntable itself. At this point, it might be stated that the wall ofthe feed tube E at the side opposite the rabbles extends below the loweredge of the main body of the tube to form a segmental shield which actsto prevent the material deposited on the table from spreading in adirection other than toward the rabbles.

The rabble bars H are arranged on a horizontal bar Hs which passesoutwardly through the furnace wall where it is anchored to a member ofthe framework C8 (Figures 2 and 3). That portion of the bar'whichextends within the furnace is suspended from an overlying member H9 bymeans of a series of eye bolts H10 arranged at suitable intervals alongsaid member and which, together with a collar H12 pinned to the baradjacent the outermost rabble, tend to hold the rabbles in their properpositions. The supporting member H9 is formed at its inner end with acollar H11 surrounding the tubular element E' and is itself in turnsupported in position by a pair of long bolts H13, H14 extendingupwardly beyond the roof of the furnace where they are secured at theirupper ends to the frame-work. The long bolt H13 more remote from thecentre'of the furnace passes through the supporting member H9 at itsouter end and is provided with a nut engaging-the lower face of thesupporting member and serving to x its position. The long bolt H14 lo-'cated near the centre of the furnace actually passes down through thetubular element E and is formed at its lower end with an eye throughwhich there extends a transverse bar E1 passing not only through thewalls of the tubular element but also through the walls of the collarH11, thus serving to anchor all of the elements together at this point.The transverse bar E1 is headed at one end, which head is engaged by anoffset portion of another bar H15 bolted to the collar H11 and whichextends horizontally and at an angle with 'respect to the baril-i8likewise to the outside of the furnace where it is anchored in position"in the framework. According to this arrangement the tubular element, atits lower end as well as the device that supports the rabbles iseffectively held against movement in all directions.

As previously stated, the calcining chamber G is closed at the top by acircular metal dome D (Figure 1) supported at its outer periphery on ametal rim D1 having a horizontal portionV resting on top of the wall C2,an upstanding vertical flange which acts to prevent the dome fromspreading under the influence of heat, and a depending ange which actsto locate the rim with respect to the circularwa-ll of the chamber andprevent its displacement. A hole D2 is providedin the centre of the domeD through The scraper element is thus which the tubular member E passesand around the edge of the hole, thedome is bent downwardly to form alip D3 which engages a collar E2 encircling the tubular member and whichis fixed thereto. This collar serves to support the domev adjacent itscentre. The dome, being metal, eliminates one of the troubles heretoforeencountered with a brick or refractory dome in that there is no spallingand consequent dropping of foreign gritty substances into-,the materialundergoing treatment.

While it is true that in prior art furnaces, the refractory roofs ofcalcining chambers have been in the form of a dome or arch, they partookof such form for a reason entirely different from that for which themetal dome of the instant structure is so shaped. A brick roof requiresan arch or dome shape in order that it be self-supporting. This isnottrue of the metal roof, since it can be made as an integral structurewith sufficient strength in itself to be selfsupporting. In other words,insofar as strength is concerned, the metal roof could just as well beilat as in the form of a dome and actually such a flat roof was triedwith the present furnace. While the flat roof was satisfactory in everyway as far as the manufacture of rouge, free from contamination, wasconcerned, it developed that after long periods of use, sagging in theroof occurred requiring suspension of operations. The longest period ofoperation without suspension for this reason was in the neighbourhood offourteen weeks. Since, however, it was desired to have the process acon- 1 tinuous one over long periods of time, a dome shaped metal roofwas resorted to, means being provided at the outer edge of the roof toprevent spreading. With this arrangement, the expansion that occurs inthe metal is evidenced by an upward movement of the dome at its centre,and it is for this reason that there is no positive connection betweenthe dome and the supporting collar E2. Thus, it will be seen that whilethe roof in its preferred form partakes of somewhat the same shape asrefractory roofs heretofore used, such shape is for an entirelydifferent purpose and causes the roof to function in an entirelydifferent way.

The gaseous products resulting from the decomposition of ferroussulphate monohydrate, namely, sulphur dioxide, sulphur trioxide andwater, lpass from the calcining chamber G through a flue J (Figure 2) toa lime filled tower K (Figure 5) wherein the sulphur oxides are absorbedbefore the gases are allowed to pass to the atmosphere. The wastegaseous products of combustion pass out through a flue L at the bottomof the furnace and the heat recovered, if desired, for use in earlierstages of the process.

Care must be taken to maintain the velocity of the gases passing fromthe calcining chamber to an absolute minimum to prevent rouge from beingcarried away. The velocity of these,

gases is increased by the evolution of SO2, SO: and H2O in the processand tends to cause a slight back pressure up the tubular feed pipe E.

H13, H14, tubular feed E, the muiiie dome D, etc.,

' are made of the special Vesuvius steel heretothe purpose. The presentimprovements in the f process and Afurnace were developed only afterconsiderable expense and experimental work and, so far asY theapplicants know, provide the only satisfactory method for producingrouge by a continuous process.

In the accompanying drawings, the invention has been shown merely by wayof example and in preferred form, and obviously many variations andmodifications may be made therein which will still be comprised withinits spirit. It is to be understood, therefore, that the invention is notlimited to any specific form or embodiment, except insofar as suchlimitations are .specified in the appended claims.

Having described our invention, we declare that what we claim and desireto secure by Letters Patent is:

1. A high temperature mufe furnace including, in combination, aturntable with metal top on which the material to be treated isdeposited, a chamber closed at the bottom by said turntable, a metalroof closing the chamber at the top, a passageway extending around thesaid chamber and above the said roof through which hot gases arecirculated, and means for preventing access of heat from the passagewayto the metal top of the turntable except by radiation from the roof ofthe chamber.

2. A high temperature muille furnace including, in combination, a tableon which the material to be treated is deposited, a chamber wherein thetable is located, a metal dome closing the chamber at the top, apassageway above the dome through which hot gases are circulated, and ametal rim at the top of the chamber upon which the dome is supported atits outer edge, said rim being formed with an upturned edge againstwhich the edge portion of thel dome abuts and acting to preventspreading in the dome despite the high temperature and consequentexpansion to which the dome is subjected.

3. A high temperature mul'llefurnace including, in combination, a tableon which .the material to be treated is deposited, a chamber wherein thetable is located, a metal dome closing the chamber at the top, apassageway above the dome through which hot gases are circulated, acentrally located and vertically arranged 'tubular device extendingthrough an opening in lthe dome and through which the furnace ischarged, means on the tubular device for supy porting the dome near itscentre, a metal rim at the top of the chamber for supporting the dome atits outer edge, said rim being arranged to limit spreading in the domeand said dome being free to move with respect to its inner support so asto accommodate expansion of the dome under the inuence of heat.

4. A high temperature mufile furnace including,

in combination, a table on which the material to be .treated isdeposited., a chamber wherein the table is located, a. one-piece metaldome closing the chamber at the top, a passageway above the dome throughwhich hot gases are circulated, a centrally located and verticallyarranged tubular device'extending through an opening in the dome andthrough which the furnace is charged, means on the tubular device forsupporting the dome near its centre, a metal rim at the top ofthechamber for supporting the dcme at its outer edge, said rim beingarranged to limit spreading in the'dome and said dome being free -tomove with respect to its inner support so as to accommodate expansion ofthe dome under kthe influence of heat.

/ 5. A high temperature muflle furnace includ ing, in combination, anexternally heated calcining chamber closed at the top by a metal domeand at the bottom by a turntable with metal top on which the material tobe treated is deposited, a series of metal rabbles overlying theturntable and adapted as the table is rotated to move the materialundergoing treatment gradually from the centre of the table to theperiphery thereof, and a tubular metal element extending upwardly fromthe centre of the table and having an opening through which thecalcining chamber can be charged from outside of the furnace.

6. A high temperature muliie furnace including. in combinatiomanexternally heated calcining chamber having a side wall, a metal domeclosing the chamber at the top, a turntable on which the material to betreated is deposited, arranged at the bottom of said chamber, acentrally located tubular element extending through said dome and havingan opening through which said calcining chamber can be charged fromoutside the furnace, means on the tubular element for supporting themetal dome near its centre, a metal rim located at the top of the sidewall of the chamber for supporting the metal dome at its outer edge andacting to limit spreading in said metal dome and Vsaid dome being freeto move with respect to its center support so as to accommodate anexpansion in the dome under the influence of heat.

'7. yA high temperature muffle furnace including, in combination, aturntable with metal top on which the material to be treated isdeposited, a series of metal rabbles overlying the turntable andadapted, as the-table is rotated, to move the material gradually fromthe centre to the periphery. a chamber surrounded by the furnace whereinthe turntable and the rabbles are located, a metal roof closing thechamber at the top, a passageway above the said roof through which hotgases are circulated, means for preventing access of heat froml thefurnace to the metal top of the turntable except by radiation from abovethe.` top, and means for feeding the material to be treated from outsidethe furnace to the centre of the table.

8. A high temperature muiiie furnace including. in combination, aturntable with metal top on -which the material to be treated isdeposited, a series of metal rabbles overlying the turntable andadapted, as the table is rotated, to move the material gradually fromthe centre to the periphery, achamber surrounded by the furnace whereinthe turntable and the rabbles are located, a metal rim with upturnededge on the chamber walls, a dome-shaped metal roof closing the chamberat the top having its edges abutting against the upturned edge of therim, a passageway above the said roof through which hot gases arecirculated, means for preventing access of heat from the furnace to themetal top of the turntable except by radiation from above the top, andmeans for feeding the material to be treated from outside the furnace tothe centre` -of the table.

9. A high temperature muffle furnace including, in combination, aturntable with metal top on which the material to be treated isdeposited, a series of metal rabbles overlying the turntable andadapted, as the table is rotated, to move the material gradually fromthe centre to thc periphery, a chamber surrounded by the furnace whereinthe turntable and the rabbles are located, a metal roof closing thechamber atthe top, a, passagewayabove the said roof through which hotgases are' circulated, heat insulating material on which the metal topof the turntable rests adapted to prevent access of heat to the metaltop except by radiation from above the top, and means for feeding thematerial to be treated from outside the furnace to the centre of thetable.

10. A high temperature muilie furnace including, in combination, aturntable with metal top on which the material to be treated isdeposited, a series of metal rabbles overlying the turntable andadapted, as the table is rotated, to `move the material gradually fromthe centre to the periphery, a chamber surrounded by the furnace where-V in the turntable and therabbles are located,

walls below the chamber adapted to prevent access of hot gases from thefurnace to the underside of the chamber, a metal roof closing thechamber at the top, a passageway above the said roof through which hotgases are circulated,` and means for feeding the material to be treatedfromoutside the furnace to the centre of the table.

ll. A high temperature mufile furnace including, in combination, aturntable with metal top on which the material to be treated isdeposited, a series of metal rabbles overlying the turntable andadapted, as the table is rotated, to move the material gradually fromthe centre to the periphery, a chamber surrounded by the furnace whereinthe turntable and the rabbles are located, walls below the chamberadapted to prevent access of hot gases from the furnace to the undersideof the chamber, a metal roof closing the chamber at the top, apassageway above the said roof through which hot gases are circulated,heat insulating material on which the metal top of the turntable restsadapted to prevent access of heat to the metal top except by radiationfrom above the top, and means for feeding the material to be treatedfrom outside the furnace to the centre V of the table.

12. A high temperature muiile furnace including, in combination, achamber surrounded by the furnace, a metal :roof closing the chamber .atthe top, a turntable with metal top on which the material to be treatedis deposited closing the chamber at the bottom, a series of'metalrabbles overlying the turntable and adapted, as the turntable isrotated, to move the material gradually from the centre of theperiphery, a passageway above the said roof through which hot gases arecirculated, means for preventing access of heat from the furnace to themetal top of the turntable except by radiation from above the top, andmeans for feeding the material to be treated from outside the furnace tothe centre of the table.

13. A high temperature muflle furnace including, in combination, achamber surrounded by the furnace, a metal roofcloslng the chamber atthe top, a turntable with metal top on which the material to be treatedis deposited closing the chamber at the bottom, a series of metalrabbles overlying the turntable and adapted, as the turntable isrotated, to move the Vmaterial gradually from the centre of theperiphery, a, passageway above the said roof through which hot gases arecirculated, heat insulating material on whichA chamber at the bottom,walls below the chamber.

adapted to prevent access of hot gases from the furnace to the undersideof the turntable, a series of metal rabbles overlying the turntable andadapted, as the table is rotated, to move the ma.- terial gradually fromthe centre of the periphery, a passageway above the said roof throughwhich hot gases are circulated, and means for feeding the material 'fromoutside the furnace to the centre of the table.

l5. A high temperature muile furnace including, in combination, achamber surrounded by the furnace, a domed metal roof 'closing thechamber at the top, a turntable with metal top on which the material tobe treated is deposited, closing the chamber at the bottom, a series ofmetal rabbles overlying the turntable and adapted, as the turntable isrotated, to move the material gradually from the centre to theperiphery, a passageway above the said roof through which hot gases arecirculated, means for preventing access of heat from the furnace to themetal top of the turntable` except by radiation from above, and atubular metal element extending upwardly from above the centre of thetable and having an opening through which the material can be fed fromoutside the furnace to the centre of the.

table.

ALLEN HARRISON. FREDERIC BARNES WALDRON.

